The present invention relates to a Catharanthus seed, a Catharanthus plant, a Catharanthus variety and a Catharanthus hybrid which contain a level of resistance to the disease Phytophthora parasitica. The present invention also relates to a Catharanthus plant product, an increased level of alkaloid content, and an increased resistance to certain insects.
Catharanthus roseus (L.) G. Don, also called periwinkle, or vinca, originates from Madagascar and belongs to the family of the Apocynaceae. This species is frequently grown annually from seed or cuttings in temperate climates for use in summer bedding or as a pot plant for the conservatory or the windowsill. C. roseus has long been grown as an ornamental in tropical regions of the world. As a consequence of its self-seediness (ability to pollinate itself and readily form mature selfed seed) it is now widely naturalized in many tropical regions. Commonly known as Madagascar periwinkle or vinca (not to be confused with the separate genus Vinca) this ornamental is commonly propagated from seed and less frequently from stem cuttings.
Periwinkle is valued for its bushy habit, large desirable flowers, tolerance to heat, drought and direct sunlight. In addition to its horticultural merits, C. roseus contains alkaloids used to retard certain diseases, such as leukemia.
Catharanthus species are well known for their production of indole alkaloids as described in Farnsworth, Lloydia 24:105-139 (1961); Sevestre-Rigouzzo, et al., Euphytica 66:151-1569 (1993). Catharanthus roseus is one of the most thoroughly investigated of plants with regard to its constituent indole alkaloids, of which more than 70 have been isolated from the whole plant as described in Balsevich and Hogge, J. Nat. Prod., 51: 1173-1177 (1988). Alkaloids are generally known as compounds biologically active against pathogens and herbivores as discussed in vanDam, et at., Oecologia 95:425-430 (1993). Indole alkaloids are potent antifeedants. Tested in a bio-assay using a 0.04% solution, vinblastine and catharanthine appeared to be the most deterrent alkaloids against the polyphagous Spodoptera larvae as described in Meisner, et al., J. Econ. Entomol. 74:131-135 (1981); Chockalingam, et at., J. Environ. Biol. 10:303-307 (1989). Periwinkle extracts have also been shown to have strong inhibitory activity against several bacterial genera. Farnsworth Lloydia 24:105-139 ( 1961) also described the anthelmintic activity of alkaloid fractions of C. roseus. Alkaloids obtained from C. roseus provide the basis of a 22-year old industry yielding well over a hundred million dollars annually as described in Raven, Diversity 9:49-51 (1993). The anticancer activity of vinblastine and vincristine, both isolated from C. roseus, is well documented in the pharmaceutical industry.
To date there has been no known resistance to Phytophthora in Catharanthus species. The principle problem with growing periwinkle is its sensitivity and susceptibility to attack by Phytophthora parasitica. Stem and crown rot caused by Phytophthora parasitica is a common problem on Catharanthus. Symptoms typically are associated with the final stages of disease development, but infected plants can support a population of the pathogen without showing visual symptoms.
Keen and Yoshikawa (in Phytophthora, Erwin et al., eds, 1983) 279-284 describe natural mechanisms of resistance to Phytophthora spp. in other crops. General resistance mechanisms against Phytophthora spp. include structural features of the host, preformed chemical inhibitors, induced structural barriers, hypersensitive reactions and phytoalexins. Keen, Adv. Plant Pathol. 65:35-82 (1982) also suggests that specific resistance to Phytophthora spp. is usually controlled by single host resistance genes. Monogenetically inherited resistance to different species of Phytophthora has been reported in several crops other than Catharanthus. Resistance has most often been found to be attributable to single, dominant alleles (Umaerus et al., in Phytophtohra, Erwin et al., eds 1983) 315-326. Colon et al., Euphytica. 66:55-64 (1983) described resistance to Phytophthora infestans in Solanum spp.
The chemical metalaxyl (which is the active ingredient of the eumycete-specific fungicities Subdue and Ridomil) has been the primary fungicide used by nursery personnel to control stem and crown rots caused by Phytophthora spp. as discussed in Ferrin, et al. Plant Disease, Vol. 76, p. 60-63, p. 82-84 (1992). While some control of the diseases is effected by the chemical metalaxyl, Ferrin, supra has found one isolate of P. parasitica from a southern California nursery which was insensitive to metalaxyl. Tolerance to metalaxyl was expressed in vivo by the isolate chosen by Ferrin, et al. supra. Furthermore, this metalaxyl-tolerant isolate appears to be as virulent as sensitive wild-type isolates. For nurseries where plants are grown in containers, widespread failures in disease control would not necessarily be expected immediately after the appearance of metalaxyl tolerance because of the low frequency with which such tolerance appears and the time needed for the pathogen population to increase and be dispersed. Widespread disease control failures occur only after a large part of the pathogen population has become tolerant to the pesticide. The rate at which this metalaxyl-tolerant population becomes established depends largely on the stability of the pesticide tolerance, the selection pressure exerted on the pathogen population, and the ability of the pathogen to disperse. Because species of Phytophthora and Pythium have been detected in recycled irrigation water in nurseries in California, the requirement that commercial nurseries in certain areas of California trap and recycle all runoff water greatly increases the risk of recycling fungicide-tolerant populations of these pathogens in those nurseries. Thus, the appearance of metalaxyl tolerance could eventually result in control failures if the treatment of recirculated water is not sufficient to eliminate propagules of Phytophthora spp. and the selection pressure due to the continued use of the fungicide metalaxyl is maintained.
The continuous use of metalaxyl as the primary means of controlling diseases caused by Phytophthora increases the likelihood for the development of insensitivity to metalaxyl (Ferrin et al., supra). History has shown new isolates of P. parasitica insensitive to new fungicides eventually will evolve and since the use of chemicals can have side effects on people using the chemicals and the environment, it is highly desirable to use a Catharanthus roseus having genetic resistance to Phytophthora spp.
A genetic resistance to Phytophthora in periwinkle, if available, could be used to reduce or eliminate the use of the chemical metalaxyl and result in increased cost efficiencies and environmental safety.